Portable reciprocating air compressor units are commonly used in a variety of applications to produce pneumatic pressure from mechanical energy that is generated from a conventional energy source such as gasoline or electricity. Such an air compressor unit normally includes a compressor pump having a reciprocating piston located within a compression cylinder, a power plant such as a motor or engine that supplies mechanical energy to the piston to cause it to reciprocate and an air reservoir for storing compressed air. The compression cylinder is configured to draw air from the environment surrounding the compressor unit and to compress the drawn air that is discharged into an air reservoir, creating a supply of air pressure having a predeterminable magnitude. A motor, engine, or other power plant is normally connected to the compressor pump to drive the reciprocating piston within a compression cylinder.
During operation of the compressor unit, a rotating crankshaft, flywheel, or other assembly connected to the reciprocating piston stores a sufficient amount of angular momentum to substantially reduce the amount of high speed torque that must be exerted by the power plant to cause the piston to reciprocate. This allows the compressor pump to devote more of the total torque output of the power plant to drawing air into the compression cylinder, compressing the air and discharging the air into the air reservoir.
However, prior to operation, the crankshaft does not rotate and therefore has no angular momentum. The power plant must therefore contend with a substantially increased low speed torque requirement to overcome the combined inertial and compression loaded resistance of the piston and other components of the compressor pump until operating speed is achieved. This increased low speed torque requirement can result in adverse system effects on the power plant such as stalling, overloading, or premature wear. It can also require that a larger or more sophisticated power plant be used to overcome the initial starting torque of the compressor unit, even if such a power plant is not actually needed to sustain reciprocation of the piston after the compressor has attained an operating speed. It follows that if the compression loaded resistance of the piston can be reduced prior to the compressor pump reaching its full operating speed, it becomes possible for the power plant to devote more total torque output to overcoming inertial resistance. This in turn can minimize the adverse effects of combined inertial and compression loading, can allow for the use of a smaller or less powerful and/or less sophisticated power plant or starting system, and can therefore lead to substantial reductions in energy usage by the compressor unit.